Receptor-like kinases (RLKs) form a large monophyletic gene family of approximately 600 members in plants (Shiu and Bleecker, 2001). They consist of proteins that contain a single extracellular domain that is thought to be the site of ligand binding, connected to a single kinase domain, via a single transmembrane domain. Upon ligand binding the kinase domain is capable of generating a phosphorylation signaling cascade. Because of the sheer size of this gene family and of the potential functional redundancy among closely related gene family members, not much is known about the function of many of these important signaling genes. What little that was known shows that RLKs have many diverse roles in plants such as, hormone perception, plant defense, plant development and cell growth.